An automotive vehicle powered fully or partially by an electric motor may be referred to as an electric vehicle (EV) or a hybrid electric vehicle (HEV). As is well known in the art, such vehicles include a high-voltage (HV) battery or batteries for supplying power to the electric motors thereof.
Such electric vehicles typically provide for charging HV batteries using a battery charger module mounted on-board the vehicle. The on-board battery charger module is provided in communication with the vehicle HV batteries and is configured to rectify AC electrical power from an electrical utility power grid for storage by the vehicle HV batteries. Such electric vehicles also include an inverter for use in converting DC voltage provided by the vehicle batteries to an AC voltage for use in powering the electric motor or motors of the vehicle. In addition, such electric vehicles may also include an auxiliary power module. These devices and modules may comprise a number of electrical components, which may include transformers, inductors, capacitors, bus bars, transistors and other components.
In a bus bar for conducting an alternating current, the AC current tends to concentrate closer to the surface of the bus bar. That is, the current density is higher towards the outer surfaces of the bus bar and lower towards the center of the bus bar. As a result, the solid cross section of an electrical conductor is only partially used when AC power is transferred through. This causes effective resistance of the bus to increase. The increase in AC resistance is more pronounced when the frequency of the AC current increases. Therefore, while this effect is experienced in 60 Hz AC utility systems, it is not substantial. However, traction inverters operating at around 1000 Hz markedly experience this effect, and wireless charging systems operating at around 85 kHz have a several fold increase in AC resistance. Increase in AC resistance causes increased power losses in the AC bus bar and hence increased temperature.
Thus, there exists a need for an improved bus bar for use in conducting an alternating current that would address the above noted issues. Such a bus bar would comprise multiple strips of electrical conductors. The thickness may be chosen based on the AC frequency and the width and number of strips may be chosen based on the total required current carrying capability. The thin strips reduce the AC resistance and gaps between the strips allow air flow to take place. Thus losses are reduced and temperature is lowered both by reduced losses and by improved convective air flow and thermal radiation.
Such a bus bar that has slots forming a ribbed structure, rather than a solid cross section, improves bus bar efficiency by lowering losses and reducing operating temperature. Such a bus bar is also lighter in weight and more compact in size than solid cross section bus bars. Such a bus bar also provides a level of efficiency for a wireless charger closer to that of an on-board charger.